Free cutting alloys



Patented Jan. 7, 1936 FREE CUTTING ALLOYS. Louis W. Kemp! and Walter A. Dean, Cleveland,

Ohio, assignors America, Pittsburgh, Pa.,

Pennsylvania No Drawing.

1933, Serial No. plication May 3,

4 Claims.

This invention-relates to aluminum base alloys and it is particularly concerned with those alloys containing silicon as a major alloy component. This application is a division of our copending 5 application Serial No. 689,880, filed September 18, 1933. Alloys disclosed but not claimed herein are claimed in our above-mentioned copending application Serial No. 689,880 and our copending applications Serial Nos. 19,608, 19,609, 19,610, 19,611, 19,612, 19,613,19,614, 19,615, and 19,616,

filed May 3, 1935.

Aluminum base alloys containing from about 3 to per cent of silicon have been widely used in cast, extruded and wrought forms because of such desirable casting characteristics as fluidity and low solidification shrinkage of the molten alloy, combined with a. good workability of the solid metal if a wrought article is to be made. The alloys also possess a low coefficient of thermal expansion and satisfactory physical proper:

ties, particularly the tensile strength and elongation. In spite of these advantageous properties, the field of utility of these alloys has been restricted because of their inherently poor machining quality and consequent increased cost of finishing articles of these alloys by machining operations such as boring, drilling, shaping, planing, or lathe-cutting. Difiiculty in machining is made evident through an excessive cutting tool wear which necessitates afrequent resharpening. Poor machinability is also manifested in a rough irregular machined surface and the tendency to form long chips that may foul the cutting tool or operating parts of the machine. Aluminum-silicon alloys are furthermore quite likely to have hard particles of elementary silicon distributed throughout the alloy matrix which seriously interfere with smooth cutting of the article being machined. These difliculties are most readily ap- 0 parent in machining operations conducted on a large scale such as the manufacture of pistons for internal combustion engines where it has been found desirable to use an expensive cutting tool material to insure long tool life and a satisfactory machined surface.

It is accordingly one of the objects of our in vention to make aluminum-silicon alloys amena- .ble to machining operations on a large scale with- 5 out encountering the disadvantages hereinbefore referred to. A specific purpose is to diminish the irregularity in cut caused by the hard silicon par-- ticles and to produce a smooth pleasing surface on the machined article. A further object is to 55 accomplish the foregoing ends without disadvanto Alumin um Company of a corporation of Original application September 18,

689,880. Divided and this ap- 1935, Serial No. 19,607

tageously affecting the physical properties of the alloy.

Our invention is predicated upon the discovery that the addition of and/or thallium to aluminum-silicon alloys containing from about 3 to- 15 per cent silicon greatly improves the machining quality of type of aluminum alloy. The

improvement is especially marked in those alloys,

containing from about 10 to 15 per cent of silicon which have heretofore been particularly diflicult to machine. We have found that the addition of from about 0.05 to 10 per cent of lead and/or thallium to aluminum-silicon alloys imparts a machinability to the alloy which renders it adaptable to all ordinary machining requirements. For the purpose of our invention, lead and thallium are substantially equivalent and are considered to constitute a' class of elements with respect to their effect upon the machining quality of aluminumsilicon alloys.

The improvement in machining characteristics referred to above may bebrought about by the addition of between about 0.05 and 10 per cent of lead or thallium to aluminum base alloys contain ing from about 3 to 15 percent silicon, but for many applications we prefer to use between about 1 and 5 per cent of either lead or thallium. The effect on machinability of these added elements is manifested by the smooth flow of chips from the article being machined, the short breakable.

chips that are produced, the absence of galling or unevenness of cut, resulting in an irregular surface of dull appearance, and'the increase in cutting speed which is possible under such favorable'conditions. As an example of an alloy possessing these properties the following composition may be cited: 12 per cent silicon, 4 per cent lead, balance substantially all aluminum.

Lead and thallium may not only be successfully used in binary aluminum-silicon alloys, but also in alloys containing copper, magnesium, manganese and the like in addition to the silicon. The action of lead and thallium in improving the machinability of such alloys appears to be substantially independent of the other alloying ingredients added to alter the character of the basic aluminum-silicon alloy. As an illustration of the benefit derived from the use of lead or they may be effectively example of the beneficial effect of lead on the machining characteristics of aluminum-silicon base alloys is found in an alloy containing about 5 per cent silicon, 0.7 per cent copper, and 0.3 per cent magnesium, the balance being aluminum. This alloy in 'cast form may be used for making cylinder heads for certain types of internal combustion engines. It is desirable that such a casting be readily machinable without diminishing the strength at ordinary or elevated temperatures. We have found that the addition of about 2.25 per cent of lead produces a marked improvement in machining quality without impairing any of the other desired properties of the alloy.

Lead and thallium may not only be used separately in alloys of the type herein disclosed, but employed in combination in certain applications. The'two elements fre quently co-act in an aluminum-silicon alloy to produce a degree of machinability not attained by an equivalent amount of either element alone. When 50 used in combination the total amount should not exceed 10 per cent and preferably less than 5 per cent is recommended. The relative proportions .of the two elements may be varied but approximately equal amounts of them generally give satisfactory results.

For certain applications it has been found de sirable to add other thallium which also serve to improve the machining quality of the alloy. The elements cadmium and bismuth belong to this class of substances and may advantageously be combined with lead and/or thallium. When so used, the metals cadmium and bismuth should be added in quantities of between about 1.5 and 6 per cent separately or in combination, the total amount in no case exceeding about 6 per cent. An alloy of this type which has been found to have a satisfactory machining quality is one containing about 12 per cent of silicon, 2 per cent of lead, and 2 per cent of cadmium, the balance being substantially all aluminu The tensile properties of the alloys herein described are not materially affected by the addition of lead and/or thallium in amounts of less than 5 per cent but there is a decline in strength .loy in solid metallic appended claims embraces elements than lead and if larger quantities are added. However, the machinabllity of the alloy lssomewhat better in such cases which compensates in part for any loss in strength. The tensile properties are likewise affected if both elements are present and 5 .the total amount of lead and thallium exceeds about 5 per cent.

The lead and thallium may be most conveniently added to the molten aluminum-silicon alform. Other methods of 10 making alloy additions practiced by those skilled in the art yield equally satisfactory results. If the amount of lead and thallium to be added exceeds about 1.5 per cent, the melt should be heated somewhat above ordinary temperatures 15 and vigorously stirred; to assure a uniform mixture. The method of adding lead and thallium to aluminum and its alloys here referred to is more fully described in copending application, Serial No. 689,885 new Patent No. 1,959,029, 20 granted May 15, 1934.

The term aluminum used herein and in the the usual impurities found in aluminum ingot of commercial grade, or picked up in the course of the usual handling 25 operations incident to ordinary melting practice.

The alloys herein disclosed may be subjected to the usual thermal treatments familiar .to those skilled in the art for the purposeof improving or altering their physical characteristics.

We claim:

1. An aluminum base alloy containing from about 3 to 15 per cent of silicon, from about 1.5 to 6 percent of cadmium and from about 0.05 to 10 per cent of lead, the balance being aluminum. 35

2. An. aluminum base alloy containing about 12 per cent of silicon, about 2-per cent of lead and about 2 per cent of cadmium, the balance being aluminum.

3. An aluminum base alloy containing from 40 about 3 to l5'per cent of silicon, from about 1 to 5 per cent of lead and from about 1.5 to 6 per cent of cadmium, the balance being aluminum.

4. An aluminum base alloy containing from about 10 to 15 per cent of silicon, from about 1 to 5 per cent of lead, and from about 1.5 to 6 per cent of cadmium, the balance being aluminum.

LOUIS W. KENIPF.

CERTIFICATE OF CORRECTION.

Patent No. 2,026,556. January 7, 1936.

LOUIS W. KEMPF, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, second column, line 4, after "of" insert lead; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 3rd day of March, A. D. 1936.

Leslie. Frazer Seal) Acting Commissioner of Patents. 

